Compound flood hazard at Lake Como, Italy, is driven by temporal clustering of rainfall events

Temporal clustering of rainfall events was the dominant driver of flooding at Lake Como between 1980 and 2020, according to an analysis of historical and meteorological data on past flooding events which highlights the importance of compound mechanisms Lake floods occur when the water level in the lake exceeds a threshold causing inundation of neighbouring shorelines. Despite the potential impacts of this type of flood on neighbouring settlements, the mechanisms and drivers that govern when lake floods occur, and particularly how they result from compound factors, remains poorly understood. Here we compile and analyze meteorological and historical data on lake floods at Lake Como (northern Italy) between 1980 and 2020. We identify seven modes of lake floods with climate-based drivers. In 70% of cases, floods are associated with a temporal clustering of rainfall. This was also the predominant trigger of the seven most severe floods. To a lesser extent, floods were driven by a single rainfall event over a water level previously increased by rainfall and/or melting. We conclude that lake floods represent a clear example of the potential for compound mechanisms to govern and exacerbate hazards.

Automated summary

An analysis of historical and meteorological data reveals that temporal clustering of rainfall events was the main driver of flooding at Lake Como between 1980 and 2020. This study highlights the significance of compound mechanisms in governing and exacerbating hazards, using lake floods as a clear example.